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1 July 2003 Ligand-Activated Signal Transduction in the 2-Cell Embryo
David P. Lu, Yan Li, Roslyn Bathgate, Margot Day, Christopher O'Neill
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Platelet-activating factor (PAF) is an autocrine trophic/survival factor for the preimplantation embryo. PAF induced an increase in intracellular calcium concentration ([Ca2 ]i) in the 2-cell embryo that had an absolute requirement for external calcium. L-type calcium channel blockers (diltiazem, verapamil, and nimodipine) significantly inhibited PAF-induced Ca2 transients, but inhibitors of P/Q type (ω-agatoxin; ω-conotoxin MVIIC), N-type (ω-conotoxin GVIA), T-type (pimozide), and store-operated channels (SKF 96365 and econazole) did not block the transient. mRNA and protein for the α1-C subunit of L-type channels was expressed in the 2-cell embryo. The L-type calcium channel agonist (±) BAY K 8644 induced [Ca2 ]i transients and, PAF and BAY K 8644 each caused mutual heterologous desensitization of each other's responses. Depolarization of the embryo (75 mM KCl) induced a [Ca2 ]i transient that was inhibited by diltiazem and verapamil. Whole-cell patch-clamp measurements detected a voltage-gated channel (blocked by diltiazem, verapamil, and nifedipine) that was desensitized by prior responses of embryos to exogenous or embryo-derived PAF. Replacement of media Ca2 with Mn2 allowed Mn2 influx to be observed directly; activation of a diltiazem-sensitive influx channel was an early response to PAF. The activation of a voltage-gated L-type calcium channel in the 2-cell embryo is required for normal signal transduction to an embryonic trophic factor.

David P. Lu, Yan Li, Roslyn Bathgate, Margot Day, and Christopher O'Neill "Ligand-Activated Signal Transduction in the 2-Cell Embryo," Biology of Reproduction 69(1), 106-116, (1 July 2003).
Received: 18 December 2002; Accepted: 1 February 2003; Published: 1 July 2003

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